This invention generally relates to wireless code division multiple access communication systems. In particular, the invention relates to channel estimation in such systems.
In code division multiple access (CDMA) communication systems, multiple communications may be simultaneously sent over a shared frequency spectrum. Each communication is distinguished by the code used to transmit the communication.
In some CDMA communication systems to better utilize the shared spectrum, the spectrum is time divided into frames having a predetermined number of time slots, such as fifteen time slots. This type of system is referred to as a hybrid CDMA/time division multiple access (TDMA) communication system. One such system, which restricts uplink communications and downlink communications to particular time slots, is a time division duplex (TDD) communication system.
In a typical TDD/CDMA communication system, communication data is sent using communication bursts. FIG. 1 illustrates a communication burst. A communication burst 16 has a midamble 20, a guard period 18 and two data fields 22, 24. The data fields carry the data of the communication burst. The guard period 18 separates the communication bursts to allow for the difference in arrival times of bursts transmitted from different transmitters. The midamble 20 separates the two data fields 22, 24 and has a known training sequence used to estimate the channel that the communication burst experiences. Using the estimated channel response, data from the data fields is recovered at the receiver.
It is desirable to have efficient approaches to perform channel estimation.